Fuel cells are electrochemical devices that are being developed for motive and stationary electric power generation. Typically each fuel cell comprises a stack of many individual electrochemical cells of like construction, in electrical connection, to provide the power requirements of the device.
One illustrative fuel cell design uses a solid polymer electrolyte (SPE) membrane, or proton exchange membrane (PEM), to provide ion transport between the anode and cathode in each electrochemical cell of a multi-cell fuel cell construction. Currently, state of the art PEM fuel cells utilize a membrane made of one or more perfluorinated ionomers such as DuPont's Nafion®. The ionomer carries pendant ionizable groups (e.g. sulfonate groups) for transport of protons through the membrane from the anode to the cathode. Gaseous and liquid fuels capable of providing protons are used. Examples include hydrogen and methanol, with hydrogen being favored. Hydrogen is supplied to each electrochemical cell anode. Oxygen (as air) is the cell oxidant and is supplied to each cell's cathode. The electrodes are formed of porous conductive materials, such as woven graphite, graphitized sheets, or carbon paper to enable the fuel to disperse over the surface of the membrane facing the fuel supply electrode. Each electrode has finely divided catalyst particles (for example, platinum particles), supported on carbon paper, to promote ionization of hydrogen at the anode and reduction of oxygen at the cathode. Protons flow from the anode through the ionically conductive polymer membrane to the cathode where they combine with oxygen to form water, which is discharged from the cell. Conductor plates carry away the electrons formed at the anode.
Electrocatalysts promote the reactions between hydrogen and oxygen to generate electricity for low temperature (for example, 80° C.) fuel cells like PEM fuel cells. Platinum is presently a preferred choice as a catalyst for the electroreduction of oxygen in acidic media. The electrocatalytic activity of Pt catalyst is dependent on many factors including the properties of the support material on which the nanosize platinum particles are carried. Suitable catalyst support particles need to provide high surface area for effective dispersion of catalyst particles and suitable electronic conductivity for efficient electrode function. Carbon black (Vulcan XC-72R) has been a widely used support for preparing fuel cell catalysts because it has provided a combination of electronic conductivity and reasonable surface area. However, the inventors herein note that many platinum nanoparticles are trapped in deep cracks within the carbon black. The trapped catalyst particles are blocked from effectively presenting necessary three-phase boundary reactive sites in the electrode, and utilization of the expensive platinum material is significantly reduced. Therefore, it is necessary to identify and prepare different catalyst support materials with surface characteristics that make better utilization of expensive electrocatalyst materials.